Mechanisms for converting a rotary motion into linear motion

ABSTRACT

The invention is a set of series-connected toggle linkages adapted to transform an input rotary motion into an output cyclic reciprocatory linear displacement having a predetermined dwell period over an arc of the input rotary motion. Each toggle linkage in a set has a mean &#39;&#39;&#39;&#39;made&#39;&#39;&#39;&#39; working position and a mean &#39;&#39;&#39;&#39;broken&#39;&#39;&#39;&#39; working position, and has its one extremity mounted on a fixed pivot axis. The other extremity of each toggle linkage represents the output drive and, except in the case of the last toggle in the set, this output extremity is directly coupled to the knee joint of the next toggle, the arrangement being such that, in the &#39;&#39;&#39;&#39;made&#39;&#39;&#39;&#39; mean position, each knee joint is driven overcenter so that there is no significant output from the toggle for a finite proportion of each cycle of rotation of the input. A second and synchronized cyclic linear motion can be derived from the same rotary input and arranged to have a dwell period which overlaps that of the first linear motion, and one of the motions can be arranged to have two dwell periods by the expedient of arranging that the toggles in the series which are simultaneously broken while the remainder is or are made for the duration of one dwell period are subsequently simultaneously made for the other dwell.

United States Patent [72] Inventor Eugen Weber FOREIGN PATENTS Hinwil, u Switzerland 225,643 5/1943 Switzerland 18/16 pp 818,518 486,135 9/1952 Canada 74/520 Flled p 1969 370,191 2 1923 Germany 74 520 [45] Patented June 15, 1971 [731 Assignees Harry Dudley Wright; Pmnary Examiner-F red C. Mattern, Jr.

Robert Ernest Leda" Ass1stantExammer-Wesley Ratl ff, l r. Geneva, Switzerland Attorney--Kenyon & Kenyon, Reilly, Carr & Chapm [32] Priority May 7, 1968 [33] Great Britain ABSTRACT: The invention is a set of series-connected toggle [31] 21517/68 mkages adapted to transform an mput rotary motron Into an output cyclic reciprocatory linear displacement having a predetermined dwell period over an arc of the input rotary motion. Each toggle linkage in a set has a mean made" work- 5 MECHANISMS FOR CONVERTING A ROTARY ing position and a mean broken" working position, and has MOTION INTO LINEAR MOTION its one extremity mounted on a fixed pivot am. The other ex 14 Chin, 7 Drawing Figs tremity of each toggle llnkage represents the output drive and,

except in the case of the last toggle in the set, this output ex- [52] US. Cl 74/520, tremity is directly coupled to the knee joint of the next toggle 18/16 the arrangement being such that, in the made mean posi- [51] Int. Cl. 13/2):5 ion, each knee joint is driven overcame,- So that there is no c si nificant out ut from the to le for a finite r0 ortion of 50 Field of Search 74/520; eagch cycle ofrgmion ofthe fi A Second andzynllhmnized 18/16 T cyclic linear motion can be derived from the same rotary input [56] References Cited gand arranged to have a dwell period which overlaps that of the lrst linear motion, and one of the motions can be arranged to UNITED STATES PATENTS have two dwell periods by the expedient of arranging that the 2,269,758 1/1942 Noronha 18/16 toggles in the series which are simultaneously broken while 2,667,788 2/1954 May et al. 74/520 the remainder is or are made for the duration of one dwell 3,142,185 7/1964 Knowles... 74/520 period are subsequently simultaneously made for the other 3,452,623 7/1969 Bastain 74/520 dwell.

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PATENTED JUN! 5 1971 SHEET 1 [1F 7 INVEN Ton EUGEN WEBER HTTO/QNE V5 SHEET l 0F 7 PATENTED JUN 1 5 ml NX QM INVENTO/Q EUGE/V WEBER 2 47TH A/EVE \w Q/ a.

PATENTED JUN] m:

SHEET 5 OF 7 W flfrann/ 9 PATENTEU JUN] 5 I97! SHEET 7 OF 7 INVENTOF? EUGEN WEBER MECHANISMS FOR CONVERTING A ROTARY MOTION INTO LINEAR MOTION This invention concerns mechanisms for converting a rotary motion into linear motion, and more particularly, for deriving a cyclic linear motion having a predetermined dwell period or periods. More specifically, although not exclusively, it is concerned with mechanisms for deriving two separate cyclic linear motions having a predetermined phase relationship, such as the motions of a mold and a ram in a machine for molding thermoelastic plastics. For convenience of description herein after, the latter practical application of the invention will be envisaged.

In a machine for molding articles in thermoelastic plastics, the ram is required to force a preformed slug of the plastic material into a product mold at a relatively high rate and then to hold the pressure for a short dwell period while the material in the mold freezes. It must then be withdrawn as quickly as possible and held back for a second dwell period during which both the product mold is opened for stripping of the formed product, and the next slug is placed in position ready for the next ramming stroke. The mold itself will also be withdrawn from the ramming position to a stripping position and returned in readiness for the next ramming stroke.

There are various ways of converting rotary motion to linear motion, including crank and pitman linkages and cam and follower mechanisms. In the former, it is difficult to derive, from a continuous rotary input, a linear motion having a dwell of long durationapproaching. say, 180 of the input rotary motionor dwells of unequal duration, coupled with a relatively large linear output displacement, even though a dwell period does not necessarily imply complete immobility. Cams can be profiled to produce a very wide range of stroke patterns including long dwell periods of complete immobility of the controlled element, but are not well adapted to the development ofa combination of high acceleration and large displacement. Cams have the additional disadvantage that their load-bearing capacity, and hence the maximum force which can be transmitted to the follower, is limited due to limitations in the available contact area, so that where high forces or shock loading are involved, the parts must be unduly large.

The use of toggle linkages for the conversion of continuous rotary motion to cyclic linear motion has the advantage that the mechanical components are simple and light in construction, and that standard components and techniques can be adopted without difficulty. The stress problems are also among the simplest to evaluate.

Furthermore, a toggle is a device having an effective lost motion" characteristic in the analysis of its dynamics when one end is journaled on a fixed pivot and the opposite end is utilized to provide the output motion. This effective lost motion is obtained when such a toggle is driven slightly overcenter, the motion of the free or output end ofthe toggle being negligible for a significant deflection of the knee joint or angular displacement of the link journaled on the fixed pivot.

In the sense that the rotary input motion has no dwell period corresponding to a dwell period in the cycle of the reciprocatory output, it is continuous from start to finish of each cyclewhich may coincide with one single revolution of the rotary input member-although the speed of rotation is not necessarily constant.

Accordingly, it is an object of the present invention to use a plurality of interconnected toggle linkages for the conversion ofa continuous rotary input drive to a cyclic linear output motion which includes one or more dwell periods.

Another object of the present invention is to couple a plurality of toggle linkages in series to form a transmission set, each having one extremity journaled on a fixed pivot axis while the other extremity provides the output motion which is transmitted to the next toggle in the set or, in the case of the final toggle, to the component to be reciprocated.

A further object of the invention is to couple the output extremity of one toggle linkage to the knee joint of the next in such a way that, during each cycle of the rotary input drive, each toggle is driven overcenter to provide a period of lost motion at its output extremity.

Yet another object is to provide a set of toggle linkages connected in series in which two or more are simultaneously driven overcenter whereby the resultant output motion of the set is substantially zero over a predetermined arc of travel of the rotary input drive.

A still further object of the invention is to provide two or more sets of series-connected toggle linkages each driving its respective reciprocatory driven component, the linkages being arranged so that dwell periods in the reciprocatory mo tions of the several driven components overlap for a predetermined duration of the common rotary input drive.

A practical embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings which relate to a ram slide and a product mold slide of a plastics molding machine, and in which:

FIGS. 1 to 7 are schematic diagrams of the toggle linkages controlling the ram and product mold slides at different points in their cycles.

The mechanism illustrated comprises a continuously rotating main drive crank I0 and a pair of colinearly reciprocable slides I2, 14, the slide 12 constituting a ram slide for carrying the ram (not shown) of a plastic molding machine and the slide 14 constituting a mold slide for carrying a product mold (not shown). The crank 10 carries a crankpin 16 which traces a circular path 18 around the axis 20 of the crank drive shaft in the direction of the arrow R. This path is divided into four sectors. From the point 1 through the point 2 to the point 3 is a first dwell sector, during which the ram and mold slides are stationary at their points of nearest approach (FIGS. 1-3). From the point 3 to the point 4 is a retraction sector during which the ram slide 12 is retracted to the outer limit of its travel but the mould slide 14 just begins to retract (FIG. 4). The third sector extends from the point 4 through the point 5 to the point 6 and constitutes a second and longer ram slide dwell period which occupies almost of the crank travel (FIGS. 4-6). The ram slide 12 remains substantially stationary in its retracted position throughout this dwell period, but during the first part thereof, between the points 4 and 5, the mould slide 14 is fully retracted (FIG. 5) and during the second part, between the points 5 and 6, the mould slide 14 is again advanced (FIG. 6) almost to its forward limit position, which it reaches when the crankpin 16 reaches the intermediate point 7 (FIG. 7) of the fourth sector. Stripping of the product from the mould occurs during the first part (4-5) of the second dwell period (46) of the ram slide. The fourth sector extends from the point 6 through the point 7 to the point 1 and constitutes the ramming stroke during which the ram slide 12 advances rapidly towards the mould slide 14 and forces the slug of moulding material into the product mold.

In each figure of the drawings, the same mechanism is shown in different successive positions throughout a complete cycle of the input rotation. The mechanism in each case includes two sets of toggles. The set marked A govern the motions of the ram slide 12, and the set marked B govern the motions of the product mould slide 14. Each toggle can pass through a unique operating position in which it is made" i.e., the two links of the toggle are collinear so that small deflections of the knee joint between the links produce no significant displacement or output motion of the free end of the toggle. In this specification, the made" position is deemed to extend over a range of positions of the knee joint such that the angle (in radians) between one link and the line drawn through the outer ends of the two links is substantially equal to the sine of that angle. The degree of approximation of the actual made position of a toggle to the unique collinear position which can be tolerated in any given case may vary according to the tolerance imposed by the circumstances of use of the mechanism.

When the toggle is not within the range of positions which are deemed to fall within the definition of the term made" as interpreted above, it is broken. In the broken" condition, deflection of the knee joint produces a significant movement of the free end of the linkage and this condition tends to a limit position in which the two links exactly overlie one another. In this position, the toggle is locked against further action under any input other than a linear input to the free end of the linkage. In the present invention, this limiting broken" position of the toggle represents an inoperative condition, and the term broken" is deemed to exclude both the aforesaid limiting condition and all approximations thereto in which the finite value of friction in practical working components of the mechanism is sufficient to preclude displacement of the free end of the toggle linkage against its normal working load by application ofthe available input force to the knee joint.

Referring now to the drawings, the crankpin 16 is coupled by links 22, 24 to the knee of the respective first toggle linkage of the two sets or trains of toggles operating the ram slide 12 and the mould slide 14 respectively. These first toggles are located on fixed pivots at AL, B1 respectively, the successive driven toggles of the set A being identified by their respective fixed pivots at A2, A3 and A4, while the second toggle of the mould slide train is located on a fixed pivot B2. The pivots A4, B2 define the path of linear reciprocation of the slides 12, 14 which are required to approach each other for a ramming operation, remain in the approach position during the first dwell period and then separate to follow the cycle of motions described above with reference to the points 1 to 7 on the path 18 traced by the crankpin 16. The toggle A] consists of links 28, 30, the link 28 being located by the pivot at A1.

The output of the first toggle A1 of the ram slide operating train has the moving end of its link 30 articulated to the second toggle A2 at the knee joint 32 thereof. The position of the fixed pivot at A2 is chosen in relation to the other parts of the linkage so that when the first toggle Al is in its nominally made mean position" indicated by the chain line a,, the toggle at A2 is in its broken position.

The toggle at A2 consists of a short link 34 pivoted on the fixed pivot A2 and a long link 36 whose free end is articulated to the knee joint 38 of the toggle at A3. This latter toggle consists of links 40, 42, the latter of which provides the output motion of the toggle at its point of articulation to the knee 44 of the fourth toggle of the train at A4. The one link 46 of the latter is mounted on the fixed pivot A4 and the other link 48 is articulated to the ram slide 12. When the toggle A1 is made, the toggles A2 and A3 are broken and the toggle A4 is made.

The mould slide toggle train B1, B2 is somewhat differently arranged in that both toggles are simultaneously made or simultaneously broken. The link 24 carried by the crankpin 16 is articulated to the toggle Bl at its knee 50, and this toggle consists oflinks 52, 54, the former being mounted on the fixed pivot B1 and the latter being articulated to the knee 56 of the second toggle B2 consisting of links 58, 60, the former being carried on the fixed pivot B2 and the latter being articulated to the mould slide 14.

The sequence of operations of the mechanism described above can be seen from a comparison of the various positions of the parts shown in FIGS. 1-7. Thus, in FIGS. 1-3, it is evident that there is no significant displacement of either of the slides 12, 14 during the period when the crank is rotated from position 1 to position 3. In a machine for moulding thermoelastic products, this period represents the freezing period in the mould while the pressure of the ram is maintained on the moulding material.

This dwell period is achieved by the positioning and proportioning of the linkage Al such that it lies in its made" mean position as defined above and as represented by the chain line a,. Although it is strictly true that any departure of the links 28, 30 from the position of strict coincidence with the axis a results in a positive displacement of the point 32-and hence transmission of this displacement through the toggles A2, A3 and A4 to the slide l2the practical effect of this displacement is minimized by the fact that the toggle A4 is also in its made" mean position over the same are of travel of the crank 10. The toggles A2 and A3 are in their broken mean positions during this period, and the extent to which these two toggles transmit the displacement of the point 32 to the point 44 can be controlled by the design and location of the various components of these two linkages. As shown in FIGS. 1-3, the angle between the shorter link 34 ofthe toggle A2 and the axis a, is of the order of 35 and the linear displacement of the output end 38 of the link 36 is proportional to the sine of the variation of this angle between the positions of the linkages shown in FIGS. 1 and 3. Since this latter is very small, the displacement of the point 38 is correspondingly small. Since the angle between the link 36 of the toggle A2 and the link 40 of the toggle A3 is approximately a right angle, the displacement of the point 44 during the first dwell period is approximately equal to the displacement of the point 38 and, since the toggle A4 is "made," displacement of the slide 12 is insignificantly.

small.

Throughout the dwell period 1-3, the linkage B behaves similarly to the linkage A to maintain the slide 14 in its forward position shown in FIGS. 1-3, since both toggles B1 and B2 are in their "made" mean positions.

Between the points 3 and 4 in the crank rotation, the linkage A displaces the slide 12. If the position of the toggles AI and A4 shown in FIG. 3 are regarded as within the limits of tolerance for the made position, it is evident that further movement of the crank 10 in the direction of the arrow R after the end of the dwell period 1-3 will begin to produce significant displacement of the free end 32 of the output link 30. This movement is not linear, since the pivot pin 32 is also the knee joint of the toggle A2, and moves in an arc of a circle struck about the fixed pivot A2..At the same time, however, the knee joint 26 of the toggle Al which experiences the input displacement from the crankpin 16, itself moves in the arc of a circle struck about the fixed pivot Al. As shown in the drawings, this necessarily imparts to the knee pivot 32 a component of upward displacement in addition to the lateral displacement. Owing to the relatively small angle between the links 30 and 34, the toggle A2 moves rapidly towards its made" position 0 (see FIGS. 4 and 5). This is reflected at the slide 12 in relatively high acceleration on the withdrawal stroke of the ram.

As shown in FIG. 4, however, the displacement of the crank 10 from position 3 to position 4 does not result in the same degree of deflection of the toggle B1 from its made" mean position, as shown by the very small angle between the link 52 and the made axis 1),. Consequently, the slide 14 is only retracted through a very small increment of its stroke during the period 3-4.

Referring now to FIG. 5, the crank is shown at position 5 in which the toggle B1 has now been broken to the maximum extent. In doing so, its output link 54 has pulled the knee 56 of the toggle B2 down to its fullest extent so that the toggle B2 is also broken. This action pulls the mould slide 14 back to its fully retracted position shown in FIG. 5. This is the stroke during which stripping of the product takes place. Meanwhile, however, the linkage A has scarcely displaced the ram slide 12. The formerly made" toggles Al, A4 are now in their broken" positions while the formerly broken toggles A2, A3 are in their made positions within the definition given above (the fully made" position being indicated by the chain lines a and a This reversal of the respective attitudes of the toggles results in the establishment of a second dwell period for the ram slide 12. Since, however, the ram is inactive during this part of the cycle, and does not have to register accurately with any other part of the mechanism, the degree of tolerance permitted during the period 4-6 can be relaxed. Nevertheless, as is seen by a comparison of FIGS. 5 and 6, a considerable arc of travel of the crank can take place before a significant displacement of the slide 12 results.

FIG. 6 shows the parts in position at the end of the second dwell period of the ram slide 12. The toggle A2 has just passed through the limit of its made" position within the definition given above. Similarly, the toggle A3 is also about to break, and the ram slide 12 is in the identical position to that shown in FIG. 4 at the commencement of the second dwell period. In fact, between the crank positions 4 and 6, the slide 12 is only displaced through the relatively small portion 12 of its total stroke. In the particular machine envisaged in this application of the present invention, the second dwell period is utilized as a transfer period for displacing a newly moulded slug from its moulding position to a position in register with the cavity of the mould on the mould slide 14.

At the same time as the ram slide 12 is displaced through the small increment of stroke 12, the linkage B has begun to resume its made position, and the slide 14 has been rapidly advanced through a relatively large increment of stroke 14 (FIG. 6). Consequently, by the time that the slide 12 has begun its ramming stroke proper, as shown in FIG. 7, the product mould 14 has been returned by the linkage B to the position in which it rests throughout the first dwell period 1- 3. In this way, the mechanism ensures that the product mould is stationary before the ram begins the moulding operation, and remains in this position after withdrawal of the ram has commenced.

Effectively, therefore, the mechanism provides, once per cycle of the input rotation, simultaneous dwell periods for two linearly mutually reciprocable slides, the dwell period of one slide 14 being of longer duration than the dwell period of the other slide 12. It also provides a second and longer dwell period for the other slide 12 over another portion of the input cycle. Furthermore, it ensures that the slides are substantially motionless throughout at least the period of overlap of the simultaneous dwell periods.

Besides ensuring accurate relative displacement of the slides in their predetermined phase relationship as noted above, the mechanism also ensures that the necessary force is transmitted to the slides l2, 14 to achieve their required accelerations and to resist the designed loads at the mould. This involves the limitation of the extent to which any one toggle linkage can break so as not to approach too closely to the critical friction angle at which the toggle cannot be made" whatever the force applied to the knee.

What I claim is:

l. A toggle linkage assembly for transforming an input rotary motion into an output cyclic reciprocatory linear motion comprising a plurality of interconnected toggle linkages, each of said linkages including a pair of links and a knee pivotally connecting each of said links together at the respective ends thereof, and each of said linkages having a fixed pivot at one end thereof;

the last of said linkages being connected at an end remote from said fixed pivot thereof to a reciprocable means for moving in a reciprocating linear motion path and the remainder of said linkage being pivotally connected at the ends remote from said fixed pivots thereof to said knee of an adjacent connected linkage; and

means connected between said knee of the first of said linkages and a rotary means for imparting a pivotal motion to said knee about said fixed pivot of said first linkage in response to a rotary motion of the rotary means whereby said last of said linkages is caused to reciprocate the reciprocable means in the linear motion path in response to the rotary motion of the rotary means.

2. A toggle linkage assembly as set forth in claim 1 wherein said plurality of linkages constitute an even number.

3. A toggle linkage assembly as set forth in claim 1 wherein each of said linkages has an alternating made and broken means working attitude, wherein said made mean working attitude the angular displacement of said links of each linkage from a collinear alignment therebetween is substantially equal to the sine ofsaid angular displacement.

4. A toggle linkage assembly as set forth in claim 3 wherein half of said linkages are in said made mean working attitude and half are in said broken mean working attitude.

5. A toggle linkage assembly as set forth in claim 3 wherein said knee of each linkage is positioned to move said knee thereof in an overcenter path with said linkage in said made mean working attitude.

6. A mechanism for moving a pair of slides in a reciprocal linear motion path from a common rotary motion comprising a first series of toggle linkages connected between the rotary motion and a first slide and a second series of toggle linkages connected between the :rotary motion and the second slide, each of said linkages having a pair of links, a knee pivotally connecting said links and a fixed pivot at one end thereof;

said first series of toggle linkages including a first linkage having said knee thereof connected to said rotary motion, a last linkage connected to the first slide at the end remote from said fixed pivot thereof, and the remainder of said linkages pivotally connect-ed at the ends remote from said fixed pivots thereof to said knee of an adjacent connected linkage; and

said second series of toggle linkages including a first linkage having said knee thereof connected to said rotary motion, a last linkage connected to the second slide at the end remote from said fixed pivot thereof, and each end of said remaining linkages remote from said fixed points being pivotally connected to said knee of the adjacent connected linkage.

7. A mechanism as set forth in claim 6 wherein said rotary motion includes a rotatable drive crank and a pair of links coupled to an end of said crank, one of said links being pivotally connected to said first linkage of said first series of toggle linkages and the other of said links being pivotally connected to said first linkage of said second series of toggle linkage.

8. In combination with a reciprocal ram and a reciprocal mold core of a product molding machine, a mechanism comprising a first series of interconnected toggle linkages connected to said ram for reciprocating said ram,

a second series of interconnected toggle linkages connected to said mold core for reciprocating said mold core, and

a common continuous rotary input drive connected in common to said first and second series of toggle linkages for actuating each said series of toggle linkages in response to a rotary motion of said drive to reciprocate said ram and said mold core in a predetermined sequence.

9. A combination as set forth in claim 8 wherein each said series of toggle linkages includes linkages having a pair of links, a knee pivotally connecting said links and a fixed pivot at one end, and wherein said knee of said first linkage of each series is pivotally connected to said rotary input drive and the remainder of said knees of said other linkages are pivotally connected to an adjacent connected linkage at the end remote from said fixed pivots thereon.

10. A combination as set forth in claim 8 wherein said ram and said mold core are disposed on a common rectilinear axis.

11. A combination as set forth in claim 10 wherein said series of linkages are disposed to reciprocate said ram and said mold core in a sequence including a first advancement of said ram and said mold core towards each other, a first dwell of said ram and said mold core, a first retraction of said ram away from said mold core, a second dwell of said ram, and a subsequent first retraction of said mold core away from said ram during said second dwell of said ram.

12. A system for driving a reciprocable ram and a reciprocal mold core in a product molding machine which includes a first series of interconnected toggle linkages connected to said ram for reciprocating said ram, a second series of interconnected toggle linkages connected to said mold core for reciprocating said mold core, and a common continuous rotary input drive connected in common to said first and second series of toggle linkages for actuating each said series, wherein said first and second series of toggle linkages are arranged to reciprocate said ram and said mold core in mutually timed cyclic reciprocatory motions along a common rectilinear axis in response to rotation of said rotary input drive in a sequence wherein said first series advances said ram towards said mold core during a first arc of travel of said rotary input drive, holds said ram in a first dwell period during a second contiguous arc of travel of said rotary input drive, retracts said ram during a third contiguous arc of travel of said rotary input drive and holds said ram substantially stationary in a second dwell period in a fourth contiguous arc of travel of said rotary input drive, and said second series advances said mold core towards said ram during said first arc of travel of said rotary input drive, holds said mold core substantially stationary at least in said first dwell period, and retracts said mold core during a succeeding arc of travel of said rotary input drive.

13. A system as set forth in claim 12 wherein during said second arc of travel of said rotary input drive at least two linkages of said first series of toggle linkages are disposed within a range of overcenter drive and a plurality of linkages of said second series of toggle linkages are disposed within a range of overcenter drive, during said third arc of travel said two linkages of said first series are outside said range of overcenter drive, and during said fourth arc of travel a plurality of other linkages of said first series are disposed within a range of overcenter drive.

14. A mechanism for deriving a cyclic linear reciprocatory motion having a predetermined dwell period in each cycle of reciprocation from a continuously rotatable input drive member comprising at least one set of toggle linkages consisting of a plurality of toggles coupled in series, each toggle comprising two links articulated at their adjacent ends by a knee joint;

a fixed pivot axis for each ofsaid linkages;

each toggle of said series having one end of one link journaled on said fixed pivot axis and the opposite end of the other link providing the output motion of said toggle;

a coupling between said rotary member and the first toggle of said series such that said knee joint is driven overcenter to an extent insufficient to produce a significant output motion of said toggle, and

an articulation between the output motion end of each toggle except the last in said series and the next toggle in such a way that the knee joint of the latter can be driven overcenter to an extent which is insufficient to produce a significant output motion of that toggle for a period equal to that of said predetermined dwell period. 

1. A toggle linkage assembly for transforming an input rotary motion into an output cyclic reciprocatory linear motion comprising a plurality of interconnected toggle linkages, each of said linkages including a pair of links and a knee pivotally connecting each of said links together at the respective ends thereof, and each of said linkages having a fixed pivot at one end thereof; the last of said linkages being connected at an end remote from said fixed pivot thereof to a reciprocable means for moving in a reciprocating linear motion path and the remainder of said linkage being pivotally connected at the ends remote from said fixed pivots thereof to said knee of an adjacent connected linkage; and means connected between said knee of the first of said linkages and a rotary means for imparting a pivotal motion to said knee about said fixed pivot of said first linkage in response to a rotary motion of the rotary means whereby said last of said linkages is caused to reciprocate the reciprocable means in the linear motion path in response to the rotary motion of the rotary means.
 2. A toggle linkage assembly as set forth in claim 1 wherein said plurality of linkages constitute an even number.
 3. A toggle linkage assembly as set forth in claim 1 wherein each of said linkages has an alternating made and broken means working attitude, wherein said made mean working attitude the angular displacement of said links of each linkage from a collinear alignment therebetween is substantially equal to the sine of said angular displacement.
 4. A toggle linkage assembly as set forth in claim 3 wherein half of said linkages are in said made mean working attitude and half are in said broken mean working attitude.
 5. A toggle linkage assembly as set forth in claim 3 wherein said knee of each linkage is positioned to move said knee thereof in an overcenter path with said linkage in said made mean working attitude.
 6. A mechanism for moving a pair of slides in a reciprocal lInear motion path from a common rotary motion comprising a first series of toggle linkages connected between the rotary motion and a first slide and a second series of toggle linkages connected between the rotary motion and the second slide, each of said linkages having a pair of links, a knee pivotally connecting said links and a fixed pivot at one end thereof; said first series of toggle linkages including a first linkage having said knee thereof connected to said rotary motion, a last linkage connected to the first slide at the end remote from said fixed pivot thereof, and the remainder of said linkages pivotally connected at the ends remote from said fixed pivots thereof to said knee of an adjacent connected linkage; and said second series of toggle linkages including a first linkage having said knee thereof connected to said rotary motion, a last linkage connected to the second slide at the end remote from said fixed pivot thereof, and each end of said remaining linkages remote from said fixed points being pivotally connected to said knee of the adjacent connected linkage.
 7. A mechanism as set forth in claim 6 wherein said rotary motion includes a rotatable drive crank and a pair of links coupled to an end of said crank, one of said links being pivotally connected to said first linkage of said first series of toggle linkages and the other of said links being pivotally connected to said first linkage of said second series of toggle linkage.
 8. In combination with a reciprocal ram and a reciprocal mold core of a product molding machine, a mechanism comprising a first series of interconnected toggle linkages connected to said ram for reciprocating said ram, a second series of interconnected toggle linkages connected to said mold core for reciprocating said mold core, and a common continuous rotary input drive connected in common to said first and second series of toggle linkages for actuating each said series of toggle linkages in response to a rotary motion of said drive to reciprocate said ram and said mold core in a predetermined sequence.
 9. A combination as set forth in claim 8 wherein each said series of toggle linkages includes linkages having a pair of links, a knee pivotally connecting said links and a fixed pivot at one end, and wherein said knee of said first linkage of each series is pivotally connected to said rotary input drive and the remainder of said knees of said other linkages are pivotally connected to an adjacent connected linkage at the end remote from said fixed pivots thereon.
 10. A combination as set forth in claim 8 wherein said ram and said mold core are disposed on a common rectilinear axis.
 11. A combination as set forth in claim 10 wherein said series of linkages are disposed to reciprocate said ram and said mold core in a sequence including a first advancement of said ram and said mold core towards each other, a first dwell of said ram and said mold core, a first retraction of said ram away from said mold core, a second dwell of said ram, and a subsequent first retraction of said mold core away from said ram during said second dwell of said ram.
 12. A system for driving a reciprocable ram and a reciprocal mold core in a product molding machine which includes a first series of interconnected toggle linkages connected to said ram for reciprocating said ram, a second series of interconnected toggle linkages connected to said mold core for reciprocating said mold core, and a common continuous rotary input drive connected in common to said first and second series of toggle linkages for actuating each said series, wherein said first and second series of toggle linkages are arranged to reciprocate said ram and said mold core in mutually timed cyclic reciprocatory motions along a common rectilinear axis in response to rotation of said rotary input drive in a sequence wherein said first series advances said ram towards said mold core during a first arc of travel of said rotary input drive, holds said raM in a first dwell period during a second contiguous arc of travel of said rotary input drive, retracts said ram during a third contiguous arc of travel of said rotary input drive and holds said ram substantially stationary in a second dwell period in a fourth contiguous arc of travel of said rotary input drive, and said second series advances said mold core towards said ram during said first arc of travel of said rotary input drive, holds said mold core substantially stationary at least in said first dwell period, and retracts said mold core during a succeeding arc of travel of said rotary input drive.
 13. A system as set forth in claim 12 wherein during said second arc of travel of said rotary input drive at least two linkages of said first series of toggle linkages are disposed within a range of overcenter drive and a plurality of linkages of said second series of toggle linkages are disposed within a range of overcenter drive, during said third arc of travel said two linkages of said first series are outside said range of overcenter drive, and during said fourth arc of travel a plurality of other linkages of said first series are disposed within a range of overcenter drive.
 14. A mechanism for deriving a cyclic linear reciprocatory motion having a predetermined dwell period in each cycle of reciprocation from a continuously rotatable input drive member comprising at least one set of toggle linkages consisting of a plurality of toggles coupled in series, each toggle comprising two links articulated at their adjacent ends by a knee joint; a fixed pivot axis for each of said linkages; each toggle of said series having one end of one link journaled on said fixed pivot axis and the opposite end of the other link providing the output motion of said toggle; a coupling between said rotary member and the first toggle of said series such that said knee joint is driven overcenter to an extent insufficient to produce a significant output motion of said toggle, and an articulation between the output motion end of each toggle except the last in said series and the next toggle in such a way that the knee joint of the latter can be driven overcenter to an extent which is insufficient to produce a significant output motion of that toggle for a period equal to that of said predetermined dwell period. 